Trawling otters



June 22, 1965 c. D. BURNEY 3,190,025

TRAWLING OTTERS Filed July 5, 1963 4 Sheets-Sheet 1 June 22, 1965 c. D. BURNEY TRAWLING OTTERS 4 Sheets-Sheet 2 Filed July 5, 1963 June 22, 1965 c. D. BURNEY 3,190,025

'I'RAWLING OTTERS Filed July 5, 1963 4 Sheets-Sheet s 1 n v e n t o r 6mm [5' 0mm: rap/v 60M BYJWAM A ttorn e y June 22, 1965 c. D. BURNEY 'I'RAWLING OTTERS 4 Sheets-Sheet 4 Filed July 5, 1965 Inventor (/Mkmss D. BUR/V5) A lforney United States Patent 3,190,025 TRAWLING @TTERS Charles Dennistoun Barney, ll Chesham Place,

London SW. 1, England Filed July 5, 1963, Ser. No. 2%),031 14 Claims. (Cl. 43-9) This invention relates to trawling otters adapted to be connected to nets trawled during fishing operations in order, by applying lateral forces to the net while being towed through the water, to open out the mouth of the net in order to gather fish therein.

The object of this invention is to provide improvements as compared with the standard type ofotter which travels on the bottom of the sea bed and is kept in place by a downward thrust of the plane driving it to the sea bed.

The invention consists in a trawling otter comprising a main lift surface, and a control surface which is adjustable to vary its angle of incidence in relation to the general direction of movement of the otter, and thereby to modify the attitude of the otter and so vary the angle of attack of the main lift surfaces, thus varying the load of the otter on its towing cable.

The type of otter proposed, when attached to the warp, automatically takes up its position horizontally from the warp and since its point of attachment to the warp is at a predetermined height above the sea bed, the otter never comes in contact with the sea bed and cannot therefor be damaged by striking an obstruction on the sea bed. This has the advantage of keeping the nets laterally open at a fixed distance between the wings of the net. When the orthodox otter tracks on the bottom, owing to its ploughing action on the sea bed the lateral opening of the net varies with the type of bottom on the sea bed. Secondly the automatic control of the after vane in the otter proposed steers the otter into its position whatever may be its direction compared with its motion through the water when the towing vessel starts from rest. Thirdly, when streaming or hauling the warps in, it is necessary for the side thrust to be reduced and for the otter to travel on the surface without porpoising so that it can be hauled up into the ship without damage.

The main lift surfaces may be a vane or vanes extending laterally from theforward end of the body, and the auxiliary control surface may be a vane extending laterally from the body and located to the rear of the main lift surfaces. The control vane may be rotatable about an axis extending from its outer tip inwards towards the body. The main and control vanes are preferably of aerofoil section.

The control .vane may be connected to a mechanical linkage whereby its angle of incidence can be adjusted, and the towing cable may be connected to this linkage in such a manner that the angle of incidence of the control vane depends upon the direction of the pull applied by the cable to the otter. Thus during a towing operation when the otter is moving at one side of, and substantially transversely of the direction of movement of the otter and net and in this position the mechanical linkage on the cable is arranged to set the inclination of the control vane (and thus of the main lift" surfaces) at such an angle that the otter provides an optimum transverse load to open the net month. On the other hand when the otter is being drawn towards the trawler the otter cable extends more or less in the same direction as that in which the otter is moving (i.e. more or less parallel to the otter body), and the cable extending in this direction, in one embodiment of the invention, operates the mechanical linkage to reduce or reverse the angle of incidence of the control vane, thereby modifying the 3,l%,025 Fatented June 22, 1965 attitude of the otter in order to reduce the angle of incidence of the main lift surfaces and thus reduce the resistance of the otter to the drawing in operation. It will thus be seen that the modification of the attitude of the utter becomes quite automatic according to whether it is performing a net-opening function during trawling operations, or (in one embodiment) is being drawn in when a trawling operation is terminated.

In modern fish trawling the tendency is to employ nets with larger mouth openings, and/or to trawl two nets simultaneously. For such a purpose it is desirable to employ buoyant otters rather than non-buoyant otters heretofore employed tending to move over or near to the sea-bed. Buoyant otters can provide a greater lift/drag ratio than otters of the kind previously used while being free from any downward reaction tending to drive them towards the sea-bed, and are thus very suitable for keeping open the mouths of larger and/or multiple nets used in modern towing."

With these considerations in mind it is preferred, in accordance with'another feature of the invention to incorporate the control system specified above in a buoyant otter.

In this preferred form of the invention a trawling otter incorporating the control means referred to above comprises a body located medially of and secured to a vane or vanes i.e. having areas extending from the body on opposite sides. Two vanes may be associated with the body in spaced tandem relation, and each. extending from the body on opposite sides. The two vanes may be of the same or difierent aerofoil sections, or single curved or plane surfaces, and may be set at different angles of incidence in relation to the fore-and-aft centre-lineof the body. The vanes may be strengthened by tubes or rods, extending, substantially parallel to the otter body, between the tips of the vanes. At the tail of the body may be provided a stabilising fin upstanding from the body in a plane perpendicular to the chordal planes of the vanes. The point of tow of the otter by a suitable line may be located on the body between the tandem vanes, and preferably positioned to be co-incident with the centre of i pressure of the two vanes in both a horizontal and a vertical direction. The vanes may be weighted at their lower ends.

Alternatively the body may be merged into the forward wing itself and the vane operated by the automatic control and attached to the trailing edge of the forward wing, together with the stabilising fin or fins thus shortening the length of the otter for use in smaller vessels.

The invention will be clearly understood from the following description of forms (given, however, merely by way of example) which it may assume, and this description will be more readily followed by reference to the accompanying drawings wherein FIGURE 1 represents in plan somewhat diagrammatically a trawling otter in operative position, in accordance with the invention, incorporating automatic attitude-control means;

FIGURES 2 and 3 represent in side elevation and plan, respectively, one form of otter in accordance with the invention;

FIGURE 4 represents in perspective another form of otter in accordance with the invention;

FIGURE 5 represents a plan View of .a horizontal section of the otter shown in FIGURE 4;

FIGURE 6 represents a transverse section along the line A-A of FIGURE 5 and FIGURE 7 represents in perspective an otter of the kind shown in FIGURES 4-6 with part of the skin of the pressure surface broken away, and the control vane of the trailing edge detached, in order to illustrate a preferred mode of construction.

As explained above the main purpose of the present invention is to construct an otter in suchia manner as to (facilitate the hauling in and streaming of the otter while ensuring that it functions correctly while being towed. The term streaming is the standard expression in trawling operations which refers to the act of lowering an otter from a traiwler into the water and allowing it to drift astern of the trawler with the net which it will extend to catch fish. For this purpose a rear vane may be adjusttable to vary its angle of incidence in relation to the direcplate 37 .is pivoted to a bracket member 38, by one apex.

A lug or arm 39 upstanding from the rear vane, and in line rearwardly with the bracket 38 and plate 37, is conneeted by a link 40 with another apex of the triangular plate 37. The towing line 41 is connected to the third apex of the plate 37. When the otter is holding nets extended during towing, the line 41 takes up the position shown in full lines in FIGURE 1, and the plate 37, link 40, lug 39 and rear vane 22 are thereby held in the positions shown in full line. When the otter is being hauled in the line 41 is in the position shown in chain lines, and rocks the plate 37 about its pivot, thereby moving the link 40, lug 39 and rear vane 22 to the dotted line positions, where the angle of incidence of the rear vane is reduced to a small, or even a negative value.

The above described means for automatic attitudecont-rol of the otter may be incorporated in buoyant otters of many different forms and a few preferred forms of otter according to this invention in which such automatic control means are incorporated are illustrated in FIG- URES 27 of the aforesaid drawings.

In the formof otter in accordance with the invention illustrated in FIGURES 2 and 3 of the drawings herewith, designed to facilitate production, the body is formed of three buoyant tubular cylindrical sections 21 with conical nose and tail members 1a, 1b, respectively, all welded together in line. A rear vane comprises three sections 22 each formed of sheet metal extending as aerofoil surfaces between spars 23, the three sections 22 being mounted upon a common rod or tube 24 which extends through an aperture in the body, and being held fast on this rod 24 by end nuts. As shown one section 22 is above the body and the other two sections below, in the operating position, when viewed in side elevation in FIGURE 2. The forward vane is in two sections 25, meeting at the line 26, each section being formed of sheet metal mounted to form aerofoil surfaces on a tubular metal frame, 27. In the 'metal sheets of each section is provided an oval aperture 28a or 2812 through which the body 21 can project when the chordal plane of the vane is at an angle to the axis of the body. The trailing edge of the forward vane is secured to the out-turned bracket ends 32 of a metal strip attached, e.g. by welding, to the body, while the leading edge of the vane is secured to a rod or tube 33 mounted [in bracket portions of a collar 34 secured round the body adjacent to the nose piece, 1a. As illustrated the length of each vane projecting downwardly from the body is greater than that projecting upwards (as seen in FIGURE 2). This provides weight distribution assisting the otter, when immersed and towed, to assume a position in which the vanes are substantially vertical FIGURE 2). If desired the lower extremities of the vanes may be weighted to assist in this effect.

The body is fitted into the aperture 28a of the upper sect-ion, and the aperture 28b in the lower section may be closed by covers 29. By providing apertures in both sections it is possible to invert the sections when fitting them to a body (and transposing the covers 29) whereby the otter can be suitable .for part or starboard use. Each end of a metal strip 30 secured e.g. by welding to the lift aerofoil surface of the vane is turned out at the edge of the 'vane to form a bracket 31, at each side of the vane, and strenghtening tubes or rods 20 extend between these brackets (to which they may be secured by bolts), and the ends of the rod 24 of the rear vane (to which they are held by the nuts previously mentioned), The tubes 20 are substantially parallel .to the body axis.

The tail 1b of the body is provided with a stabilising fin comprising a metal tube 13, supporting a metal sheet '14 which may be flat, as shown. The body is provided at 12 with a block for the bracket 38 and plate 37, as shown in FIGURE 1, to which a towline can be connected. The plate 37 is connected by a link 40 to a lug or arm 39 on the rear vane 22, 23, as described above with reference to FIGURE 1, in order that the angle of incidence of the rear vane shall be automatically controlled in accordance with the direction of tow, as described. For the sake of clarity these last mentioned components are not shown in FIGURES 2 and 3. The centre of tow at 12 is substantially coincident with the resultant centre of pressure of the vanes.

Guard means to protect the nose piece 1a and to prevent entanglement of a warp towing the otter may comprise two curved rods or tubes 3'5 in relatively crossed relationship extending, across and in front of the nose piece, from a bracket 36 on one side of the collar 34, to a point adjacent to the leading edge of the main vane on the opposite side of the body. The end of the guard member is preferably not attached to the vane.

An otter such as shown in FIGURES 2 and 3 is used as a free-flying otter, and is connected by a single warp 41 running from the plate 37 to an upper corner of the mouth of a trawling net. One convenient net arrangement using otters in this manner is illustrated in FIGURE 1 of the specification of copending patent application No. 293,032 filed on July 5, 1963.

When an otter such as described above is so connected to a net by a cable linked to the point of tow at 12, and, with the net, is towed through the water by a trawler, the otter, under the resulting gravitational and hydrodynamic forces assumes a stable position in which spans of the vanes is. the transverse dimensions perpendicular to the axis of the body 21, are substantially vertical. The lift of the vanes urges the otter away from the net, which is thus drawn to one side of the line of advance of the trawler and the mouth of the net is pulled wide open. The weight dispositions of the otter, and the fin area 14 serve to prevent the otter from diving to the sea bed.

In another form of otter in accordance with the invention shown in FIGURES 4-7 of the aforesaid drawings the main lift and control surfaces are brought together, and the body effectively eliminated. The otter as a whole is formed in aerofoil section comprising a main lift member 42 fitted with a pivoted rudder member 43 at its trailing edge. Each member may be formed of foamed plastic, expanded and solidified in a thin outer envelope, which may be fitted with, and internally strengthened near its leading edge by, an embedded tube or rod 45.

A recess in the main member 42 in the area of the centre of pressure of the otter accommodates a skid 47 secured in the recess. This skid has bearing blocks 48 mounted on support plates 49 between which blocks extends a shaft 50 pivotal-1y mounting a cranked,twin-limbed towing block 51. Limbs of the towing block projecting from the skid 47 on the pressure side of the otter carry a pin 52 linking the towing cable to the block 51. The outer limbs of the cranked towing block 51 extend towards the trailing edge of the otter, and have pivoted thereto one end of a push-pull rod 53 which extends through a tunnel 54 in the main member 42 and at its other end is pivotally connected to a tiller arm 55 upstanding from the rudder 43 on the suction side of the otter. The pushpull rod 53 is preferably formed of two or more relatively adjustable parts to allow modification of length as desired. The underside edge of the otter may be loaded with a ballast shoe in the form of a heavy metal plate 56 detachably secured to the lower side edge of the vane.

It will be understood that the inclination of the rudder 43 is modified by the rod 53 according to the direction of pull on the towing line 41, and the otter accordingly assumes automatically the desired angles of attack when being streamed out or hauled in, and when in use to hold open the net mouth, as described above.

In the forms of otter described above in accordance with the invention the body and vanes are hollow, but in alternative otters in accordance with the invention the hollow body and/ or vanes may be packed internally with a material of low density and high load-bearing strength, to increase the strength and buoyancy of the otter. In FIGURE 7 is represented a mode of construction of the form of otter shown in FIGURES 4-6, having an internal packing of such material. A series of spar members 101 of aerofoil section (conveniently stamped from metal sheet) are held in parallel spaced relationship by transverse strip web members 109, which are butt welded to the spar members, the whole forming a cell-like grid structure. The rod or tube 45 runs through the spar members 101 near to the leading edges thereof and is welded in position. The sheet metal skin 42 is welded to the suction (convex) side of this cell structure. The box-like cells thus formed are filled with the selected material, which is preferably a foamed plastics material such as rigid foamed polyurethane. Such a material may have a load-bearing capacity of 1000 lbs. or more per square inch, and a density, under such a load, of about 20 lbs. per cubic foot.

The cells may be filled with this material in either of two Ways. Blocks 192 may be separately preformed in moulds (in which the plastic is foamed and allowed to set) of the same shape as the cells of the otter structure, and these preformed blocks may be fitted into the cells as shown in FIGURE 7, whereafter the cells are closed by welding on the skin 42 of the pressure surface to close the cells. Alternatively the skin 42 may be welded to the pressure surface, and apertures formed in this skin giving access to the various cells. These closed cells are then filled with the foamed plastic material in liquid or semi-liquid form, injected through the apertures into each cell, and the material is allowed to set to a rigid state. The apertures in the skin may then be closed by welding on small cover discs or the like. The control vane 43 is made in the same way by loading a cell structure with preformed blocks or with liquid filling ma terial. The selected material to form the blocks or to be injected, should, when rigid, have high thermal stability (being able to withstand repeated freezing and thawing) and should be inert to and/or not affected by organic liquids, such as benzene, paraffin, oil or petrol, or sea water or acids, or subject to air-pollution. A number of suitable plastics are well-known, and as stated above one such material is polyurethane. The packed cell construction described allows thinner sheet metal to be used for the skin 42 without loss of overall strength, and thus allows reduction in size of the otter body, or of the otter as a whole, without loss of net buoyancy.

From the above description it will be seen that the invention provides an eflicient and powerful otter for trawling purposes, but it should be understood that the invention is not limited solely to details of the form described above, which may be modified, in order to meet various conditions and requirements encountered, without departing from the scope of the invention.

What I claim is:

1. A trawling otter comprising a main lift surface, an associated control surface adjustable during towing of the otter to vary its angle of incidence in relation to the general direction of movement of said otter, and thus to modify the angle of attack of said main lift surface, a connecting member for a towline, pivotally mounted in said otter, and a link between said connecting member and said control surface, whereby the angular position of said control surface is automatically adjusted by said link in accordance with the angular position taken up by said pivoted connecting member, in dependence upon the direction of pull applied to said connecting member, by the towline connected thereto, during a towing operation.

'2. A trawling otter according to claim I wherein the main lift surface is of aerofoil section.

3. A trawling otter according to claim 1 wherein the control surface is pivotally attached to the main lift surface near to the trawling edge of said main lift surface.

4. A trawling otter according to claim 1 comprising a main lift surface of aerofoil section, a control surface forming a section of said main lift surface pivotally mounted in a recess at the trailing edge of said main lift surface, a towing block mounted in said main lift surface adjacent to the centre of pressure thereof, a towing plate pivotally mounted in said towing block, a. connecting link extending between one point of said towing plate and said control surface, and means at another point of said towing plate for connecting a towline thereto.

'5. A trawling otter according to claim 1 wherein the main lift surface comprises an internal frame, and a skin of external sheet material stretched over the frame.

6. A trawling otter according to claim 1 wherein the main lift surface comprises a frame of strip material forming an assembly of cells, an expanded synthetic resin in said cells, and an external skin of sheet material closing said cells and forming an outer covering on the said main lift surface.

7. A trawling otter comprising a cylindrical body, a main lift surface, attached to the forward end of said body and extending from opposite sides thereof, an associated control surface attached to the rear end of said body and extending from opposite sides thereof, said control surface being adjustable during towing of the otter to vary its angle of incidence in relation to the general direction of movement of said otter, and thus to modify the angle of attack of said main lift surface, a connecting member for a towline, pivotally mounted in said main lift surface, and a link between said connecting member and said control surface, whereby the angular position of said control surface is automatically adjusted. by said link in accordance with the angular position taken up by said pivoted connecting member, in dependence upon the direction of pull applied to said connecting member by the towline connected thereto during a towing operation.

8. A trawling otter according to claim 7, wherein said main lift surface and said control surface extend a greater distance from one side than from the other side of said body.

9. A trawling otter according to claim '7 wherein the said body extends through an aperture in said main lift surface.

10. A trawling otter according to claim 7 wherein said main lift surface comprises adjacent apertures and a body adapted to extend through and be secured in either of said apertures, as desired, in order to form an otter suitable for port or starboard towing.

111. A trawling otter according to claim 7 comprising on each side of the otter a strengthening strut secured to, and extending between, the outer edge of said main lift surface and of said control surface.

12. A trawling otter according to claim 7 comprising attached to said body adjacent to its rear end, a fore-andaft stabilizing fin projecting from the body in a plane substantially perpendicular to the span of said main lift surface.

'13. A trawling otter according to claim 7, and a frame having internal spars, an external skin stretched on the frame, said main lift surface being the surface of said eX- ternal skin and being of aerofoil section.

14. A trawling otter according to claim 7, and a common shaft extending through said body and projecting from both sides thereof, a plurality of sections pivotally mounted on said shaft, said control surface being defined by said sections.

References Cited by the Examiner FOREIGN PATENTS 550,326 12/22 France. 5 295 1903 Great Britain. 19,173 1910 Great Britain. 27 1,218 5/27 Great Britain.

ABRAHAM G. STONE, Primary Examiner. 10 FfRAY CHAPFEIJL, Examiner. 

1. A TRAWLING OTTER COMPRISING A MAIN LIFT SURFACE, AN ASSOCIATED CONTROL SURFACE ADJUSTABLE DURING TOWING OF THE OTTER TO VARY ITS ANGLE OF INCIDENCE IN RELATION TO THE GENERAL DIRECTION OF MOVEMENT OF SAID OTTER, AND THUS TO MODIFY THE ANGLE OF ATTACK OF SAID MAIN LIFT SURFACE, A CONNECTING MEMBER FOR A TOWLINE, PIVOTALLY MOUNTED IN SAID OTTER, AND A LINK BETWEEN SAID CONNECTING MEMBER AND SAID CONTROL SURFACE, WHEREBY THE ANGULAR POSITION OF SAID CONTROL SURFACE IS AUTOMATICALLY ADJUSTED BY SAID LINK IN ACCORDANCE WITH THE ANGULAR POSITION TAKEN UP BY SAID PIVOTED CONNECTING MEMBER, IN DEPENDENCE UPON THE DIRECTION OF PULL APPLIED TO SAID CONNECTING MEMBER, BY THE TOWLINE CONNECTED THERETO, DURING A TOWING OPERATION. 